AD7606 IIO Multi-Channel Simultaneous Sampling ADC Linux Driver

Supported Devices

Reference Circuits

Evaluation Boards

Description

This is a Linux industrial I/O (IIO) subsystem driver, targeting multi channel, dual interface serial/parallel interface ADCs.
The industrial I/O subsystem provides a unified framework for drivers for many different types of converters and sensors using a number of different physical interfaces (i2c, spi, etc).
See IIO for more information.

Example platform device initialization

For compile time configuration, it’s common Linux practice to keep board- and application-specific configuration out of the main driver file, instead putting it into the board support file.

For devices on custom boards, as typical of embedded and SoC-(system-on-chip) based hardware, Linux uses platform_data to point to board-specific structures describing devices and how they are connected to the SoC. This can include available ports, chip variants, preferred modes, default initialization, additional pin roles, and so on. This shrinks the board-support packages (BSPs) and minimizes board and application specific #ifdefs in drivers.

The reference voltage may vary between boards and models. The platform_data for the device's “struct device” holds this information.

/**
* struct ad7606_platform_data - platform/board specifc information
* @default_os: default oversampling value {0, 2, 4, 8, 16, 32, 64}
* @default_range: default range +/-{5000, 10000} mVolt
* @gpio_convst: number of gpio connected to the CONVST pin
* @gpio_reset: gpio connected to the RESET pin, if not used set to -1
* @gpio_range: gpio connected to the RANGE pin, if not used set to -1
* @gpio_os0: gpio connected to the OS0 pin, if not used set to -1
* @gpio_os1: gpio connected to the OS1 pin, if not used set to -1
* @gpio_os2: gpio connected to the OS2 pin, if not used set to -1
* @gpio_frstdata: gpio connected to the FRSTDAT pin, if not used set to -1
* @gpio_stby: gpio connected to the STBY pin, if not used set to -1
*/

Example platform_device initialization / parallel interface

For the memory mapped parallel interface option, the user must specify the physical base address where the AD7606 is mapped into. A system IRQ number for the AD7606 BUSY indicator signal must be specified.

Example spi_board_info initialization / serial interface

Declaring SPI slave devices

Unlike PCI or USB devices, SPI devices are not enumerated at the hardware level. Instead, the software must know which devices are connected on each SPI bus segment, and what slave selects these devices are using. For this reason, the kernel code must instantiate SPI devices explicitly. The most common method is to declare the SPI devices by bus number.

This method is appropriate when the SPI bus is a system bus, as in many embedded systems, wherein each SPI bus has a number which is known in advance. It is thus possible to pre-declare the SPI devices that inhabit this bus. This is done with an array of struct spi_board_info, which is registered by calling spi_register_board_info().

Depending on the converter IC used, you may need to set the modalias accordin
gly, matching your part name.
It may also required to adjust max_speed_hz. Please consult the datasheet, for maximum spi clock supported by the device in question.

Hardware configuration

Driver testing

Each and every IIO device, typically a hardware chip, has a device folder under /sys/bus/iio/devices/iio:deviceX.
Where X is the IIO index of the device. Under every of these directory folders reside a set of files, depending on the characteristics and features of the hardware device in question.
These files are consistently generalized and documented in the IIO ABI documentation. In order to determine which IIO deviceX corresponds to which hardware device, the user can read the name file /sys/bus/iio/devices/iio:deviceX/name. In case the sequence in which the iio device drivers are loaded/registered is constant, the numbering is constant and may be known in advance.

Set input range to 10Volt

Show scale

Description:
scale to be applied to in0_raw in order to obtain the measured voltage in millivolts.

This specifies any shell prompt running on the target

root:/sys/bus/iio/devices/iio:device0> cat in_voltage_scale
0.152

Show channel 2 measurement

Description:
Raw unscaled voltage measurement on channel 2

This specifies any shell prompt running on the target

root:/sys/bus/iio/devices/iio:device0> cat in_voltage2_raw
5789

U = in2_raw * in_scale = 5789 * 0.152 = 879,928 mV

Trigger management

If deviceX supports triggered sampling, it’s a so called trigger consumer and there will be an additional folder /sys/bus/iio/device/iio:deviceX/trigger. In this folder there is a file called current_trigger, allowing controlling and viewing the current trigger source connected to deviceX. Available trigger sources can be identified by reading the name file /sys/bus/iio/devices/triggerY/name. The same trigger source can connect to multiple devices, so a single trigger may initialize data capture or reading from a number of sensors, converters, etc.

Trigger Consumers:
Currently triggers are only used for the filling of software ring
buffers and as such any device supporting INDIO_RING_TRIGGERED has the
consumer interface automatically created.

Description: Read name of triggerY

This specifies any shell prompt running on the target

root:/sys/bus/iio/devices/triggerY/> cat name
irqtrig56

Description: Make irqtrig56 (trigger using system IRQ56, likely a GPIOIRQ), to current trigger of deviceX

Buffer management

The Industrial I/O subsystem provides support for various ring buffer based data acquisition methods.
Apart from device specific hardware buffer support, the user can chose between two different software ring buffer implementations. One is the IIO lock free software ring, and the other is based on Linux kfifo.
Devices with buffer support feature an additional sub-folder in the /sys/bus/iio/devices/deviceX/ folder hierarchy. Called deviceX:bufferY, where Y defaults to 0, for devices with a single buffer.

Every buffer implementation features a set of files:

length
Get/set the number of sample sets that may be held by the buffer.

enable
Enables/disables the buffer. This file should be written last, after length and selection of scan elements.

scan_elements
The scan_elements directory contains interfaces for elements that will be captured for a single triggered sample set in the buffer.

in_voltageX_type / in_voltageX-voltageY_type / timestamp_type:
Description of the scan element data storage within the buffer
and therefore in the form in which it is read from user-space.
Form is [s|u]bits/storage-bits. s or u specifies if signed
(2's complement) or unsigned. bits is the number of bits of
data and storage-bits is the space (after padding) that it
occupies in the buffer. Note that some devices will have
additional information in the unused bits so to get a clean
value, the bits value must be used to mask the buffer output
value appropriately. The storage-bits value also specifies the
data alignment. So u12/16 will be a unsigned 12 bit integer
stored in a 16 bit location aligned to a 16 bit boundary.
For other storage combinations this attribute will be extended
appropriately.

in_voltageX_index / in_voltageX-voltageY_index / timestamp_index:
A single positive integer specifying the position of this
scan element in the buffer. Note these are not dependent on
what is enabled and may not be contiguous. Thus for user-space
to establish the full layout these must be used in conjunction
with all _en attributes to establish which channels are present,
and the relevant _type attributes to establish the data storage
format.

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